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BIOLOGICAL MOLECULES
Testing for biological molecules
 Test for reducing sugars
Add 2cm3 of Benedict’s solution to 2cm3 of glucose solution and shake the mixture
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If reducing sugars is present, the colour of the solution change from blue to brick-red
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Test the resulting solution with
Benedict’s solution in a water bath
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Add a few drops of I2 /KI solution
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

Test for fats[Emulsion Test]
Add 2cm3 fat or oil to a test tube containing 2cm3 absolute ethanol
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Add an equal volume of cold water
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

Test for proteins[Biuret Test]
Add 2cm3 protein solution to a test tube
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Add 2 drops of 1% CuSO4 solution and mix
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α-glucose

β-glucose

Carbohydrates [Cx(H2O)y]
-Substances whose molecules contain carbon, hydrogen and oxygen atoms
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Functions:
-Used as building blocks for larger molecules
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Structure of monosaccharides
e
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Glucose, C6H12O6



Disaccharides(Double sugars) – [C12H22O11]
-Formed by condensation reactions between two monosaccharides(monomers)
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-Bond that is formed is called glycosidic bond
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g
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E
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Sucrose
-Hydrolysed back to simple sugars to give energy
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-Tasteless, insoluble and are non-reducing sugars
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g
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The fatty acids tails are non-polar and hydrophobic and have no uneven distribution of electrical
charges
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Functions


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
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Used as energy storage compounds by plants, animals and fungi
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Stored around delicate organs, protecting them from shock
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Provide metabolic water to some animals in desert
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Prevent hydrophilic substances from passing through
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Structure of amino acid

Formation and breakage of peptide bond



Primary structure

It is the actual sequence of amino acids in a chain
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

Secondary structure

It is the way in which the amino acid chain is organised
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α-helix is found in keratin of hair, nails, claws, beaks, feathers, horn and also in
vertebrate skin
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Both α-helix and β-pleated sheet have hydrogen bonding in between them
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

Quaternary structure
The association of different polypeptide chains is the quaternary structure of the
protein
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g
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The chains are linked by cross-bridges and so form very stable molecules
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e
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Keratin in hair, Outer layers of skin, collagen

Collagen
It is a fibrous protein found in tissues requiring physical strength
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g
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It is extremely strong and stable
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Features:




It is largely a repeat unit of the amino acid sequence gly-pro-ala, which forms and
unbranched polypeptide
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A every third amino acid is relatively small and compact, the helix produced is
tightly wound
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Globular proteins
They are protein molecules that fold onto a roughly spherical 3D shape
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g
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They are partly soluble in water
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Two of these chains, called α-polypeptides, are identical and each consists of 141 amino acids
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Each polypeptide chain is folded into a compact shape and all 4 are linked together to form an
almost spherical haemoglobin molecule
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The hydrophilic groups tend to orient themselves pointing outwards
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Associated with each polypeptide is a haem group – which contains Fe2+ ions, which is a
prosthetic group
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Fibrous proteins
Repetitive regular sequences of amino acids
Actual sequences may vary slightly between 2
example of the same protein
Polypeptide chains form long parallel strands
Length of chain may vary in 2 examples of the
same protein
Stable structure
Insoluble
Support and structural functions
E
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collagen, keratin

Globular proteins
Irregular amino acid sequences
Sequence highly specific and never varies between
2 examples of the same protein
Polypeptide folded into a spherical shape
Length always identical in 2 examples of the same
protein
Relatively unstable structure
Soluble
Metabolic functions
E
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enzymes, some hormones (insulin) and
haemoglobin

Water
In a water molecule, the oxygen atom is negatively charged while the hydrogen atom is positively
charged
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Hence, water molecules have an electrostatic attraction for each other
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Properties of water:
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Water has a high specific heat capacity
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It has high latent heat of vaporisation
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Water is a liquid

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